Minesweeper LeetCode solution in C++

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class Solution {
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 public:
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  int m, n;
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  vector<vector<char>> updateBoard(vector<vector<char>> &board, vector<int> &click) {
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    if (board[click[0]][click[1]] == 'M') {
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      board[click[0]][click[1]] = 'X';
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      return board;
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    } else {
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      m = board.size(), n = board[0].size();
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      dfs(click[0], click[1], board);
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    }
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    return board;
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  }
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  const int dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
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  const int dy[8] = {0, -1, 0, 1, 1, -1, -1, 1};
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  void dfs(int cr, int cc, vector<vector<char>> &board) {
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    int count = 0;
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    for (int i = 0; i < 8; i++) {
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      int nr = cr + dx[i], nc = cc + dy[i];
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      if (nr < 0 || nr >= m || nc < 0 || nc >= n || board[nr][nc] != 'M') continue;
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      count++;
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    }
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    if (count != 0) {
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      board[cr][cc] = '0' + count;
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      return;
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    } else {
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      board[cr][cc] = 'B';
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      for (int i = 0; i < 8; i++) {
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        int nr = cr + dx[i], nc = cc + dy[i];
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        if (nr < 0 || nr >= m || nc < 0 || nc >= n || board[nr][nc] != 'E') continue;
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        dfs(nr, nc, board);
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      }
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    }
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  }
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};